Mineral lubricating oil additive



IWINERAL LUBRICATING OIL ADDITIVE No Drawing. Application March 28, 1952, Serial No. 279,205

5 Claims. (Cl. 252-47) The present invention relates to the use of dialkyl phenothiazines as oil soluble ashless detergent additives for mineral lubricating oils.

In accordance with the presentinvention, the higher alkyl derivatives of phenothiazine have been found to be excellent additives for mineral lubricants employed ininternal combustion engines. These additives are useful in maintaining cleanliness of engines operating under severe conditions, i. e., in minimizing formation of coke-like deposits, varnish and the like on various engine parts.

Phenothiazine has been suggested as antioxidant and corrosion inhibiting additive for ester, polyester, polyether, and other synthetic lubricants. However, in con trast to the eifect of alkyl phenothiazines in mineral lubricants, the presence of phenothiazine in synthetic crankcase lubricants actually promotes deposit formation in internal combustion engines operating under severe conditions. This effect has greatly detracted from its utility. henothiazine has also been suggested as a corrosion inhibitor for mineral lubricants, very small concentrations being used for this purpose. However, phenothiazine does not aid in maintaining engine cleanliness when used in such compositions.

In view of the above matters, it was quite surprising to find that the higher alkyl phenothiazines arequiteelfective. detergent additives for mineral motor oils and yet show substantially no corrosion inhibition properties. They are particularly useful as ashless detergents since they leave no deposits in the combustion chamber. This is. a.

valuable property in the case of aviation lubricants where the presence of ash may lead to complete destruction of a piston in a matter of minutes due to preignition. I

Moreover, phenothiazine and its lower alkyl derivatives are insoluble in mineral base lubricants in substantial concentrations and the usual solutizers havefailed to increase their solubility to a useful level. However the higher alkyl phenothiazine derivatives of the resentirn vention are soluble in effective concentrations in mineral lubricants over a Wide range of temperatures thatwould normally be encountered in storage, transportation and use.

The reason for the different effects obtained when using phenothiazine and higher alkyl phenothiazines in mineral and synthetic lubricants is not understood. While it is not desired to be limited as to any theoryof action, ob'viou'sly such compounds act by entirely different mecha: nisms. For example, in the case of synthetic and mineral lubricants, phenothiazine in small concentrations may in= hibit formation of acids, hydroper'oxidesand other corro sive substances that might otherwise form through QXidZif tion but exhibits no detergency characteristics On the other hand, the compounds of this invention evidently have little effect on the formation of corrosive materials but they undoubtedly retard formation of condensation and polymerization products that lead to varnish and coke-like engine deposits. They may also help maintain engine cleanliness by keeping such oil insoluble materials in suspension in the oil.

tates Patent I be employed in. the oil compositions.

whereinthe R groups are alkyl radicals, each having in the range of 4 to 16 carbon atoms, preferably 6 to 12 carbon atoms. The R groups may be similar or dissimilar but those that are identical in structure are preferred from the standpoint of ease of preparation. They are generally located in the para positions with respect to the nitrogen group, because of their relative ease of preparation. The R groups may be straight chain or branched in structure; branched groups are usually preferable from the standpoint of improving oil solubility. Specific alkyl groups include butyl, isopentyl, n-hexyl, tert-octyl, n-decyl, dodecyl and the like.

The dialkyl phenothiazines are readily prepared by analogous procedures used for making phenothiazine. For example, a dialkyl diphenyl amine may be treated with sulfur at an elevated temperature, such as one in the range of about 300-400 F. for a suificient time to complete the reaction. The reaction may be carried out in the presenceof a catalyst such as iodine. The reaction products may be purified by washing with suitable solvents, crystallization, recrystallization and the like procedures.

The dialkyl phenothiazine may be blendedin mineral lubricating oils in amounts in the range of about 0.2 to 5% by weight, the upper limit being restricted to some extent by the solubility of the particular compound being used. Thus, the dibutyl derivatives will generally be soluble to the extent of only about 1.0% whereas the higher alkyl derivatives are soluble to a greater extent. A preferredconcentration is in the range of about'0.5 to 1.5% by weight.

. Theadditives of the present inventionare particularly suitable for. aviation engine lubricants, although they will find use as additives for other types of combustion engine lubricants, diesel lubricants, etc. The lubricating oil base stocks may be derived from petroleum distillates and residuals refined by conventional means. Other agentsmay Such agents include pour point depressants, viscosity index improvers, oiliness agents and the like. i

The invention will be more fully understood-by refer ence to the following examples. These examples, however, are'given for the purpose of illustration only and are not to be construed as limiting the scope: of the present invention in any way.

Example I.-Preparati0n of dioczyl phenothiazine 470 g. (1.2 mols) of p,p-diisooctyl diphenyl amine, 76.8 g, (2.4 mole) of sulfur and 4 g, iodine (employed as a catalyst) were mixed in a three-neck flask andwere heated at a temperature of 340-360 F. for 1.5 hours. The mixture was then cooled, diluted with three volumes of hexanesat 210 F., heated to boiling, and filtered while hot thru Hi-flo diatomaceous filter aid. The filtrate was thenxcooledto form crystals which were separated by.

filtration. The crystals were then dissolved in fresh hexane, a small amount of carbon black was added, and the mixture cooled to crystallize the product. The crystals wereithen recovered by filtration and washed With additional hexane. The product, p,p--diisoocty1 phenothiazine was a white, crystalline material having a melting point of "167 to 168C and nitrogen and sulfur contents of 3.11 weight percent and 7.36 weight percent, respectively.

Example II.-Mineral oil solubility tests The solubility of phenothiazine and of the dioctyl phenothiazine of Example I in mineral lubricating oils was determined in a series of tests. The tests were carried out employing as a lubricant base stock a Mid-Continent, solvent extracted aviation lubricating oil having a viscosity (Saybolt) at 210 F. of about 100 seconds.

The solubility of phenothiazine was determined by blending a desired amount of it in the base oil at a temperature of about 150 F., at which temperature the material was soluble, cooling the mixture down to 40 F., and observing the resulting oil blend. A blend containing 0.1% by weight phenothiazine remained clear for six months whereas blends containing in the range of 0.2 to 0.5 weight percent of this compound became cloudy within three to nine days.

Oil blends were prepared containing 0.5% phenothiazine and 0.5% of various solubilizers including Lorol B alcohol (Cm-Cm alcohols), diisooctyl adipate, dibutyl phthalate and dioctyl phthalate. In each case, the oil blends contained sediment or were hazy or cloudy within from two to ten days at 40 F.

The dioctyl phenothiazine of Example I was tested for solubility characteristics as above. An oil blend containing 1% by weight of this material remained clear for 30 days at a temperature. of 40 F., after which the test was discontinued. This same blend remained clear for 2 months at both room temperature and 120 F., after which the tests were discontinued. A blend containing 1.5% of this compound was clear after 60 days at room temperature. A blend containing 2% of the product showed slight sediment in 7 days at room temperature.

Example IlI.Aviatin C. F. R. engine evaluation A portion of the dioctyl phenothiazine of Example I was evaluated as an additive in a solvent extracted Mid- Continent aviation oilbase stock having a viscosity of 210 F. of about 100 Saybolt seconds. In one experiment, the base stock per se was tested, and in another the base stock containing 1% of dioctyl phenothiazine was tested. The test consisted of operating the aviation C. F. R. engine for 25 hours at 1800 R. P. M. and 4 brake horsepower. wherein a perfectly clean surface is given a rating of 0 and a rating of is given to the worst condition that could be expected. The results are shown in the following table.

Additive in oil Over- Ring Var- Piston Ring Pin base stock all zone nish understickreli head ing None 2. 6 6. 0 3. 3 4. 0 3. 1 4. 6 Dioctyl phenothiazine, 1.0 wt. percent 1. 6 2.9 2.4 1.0 2.5 3.8

Example IV.Laus0n engine test on synthetic lubricant.

Phenothiazine was tested as an additive for a synthetic lubricant. The synthetic lubricant base stock employed was a Ca OX0 adipate prepared by esterifying adipic acid with Cs OX0 alcohol (from catalytic oxonation of C7 olefins with hydrogen and carbon monoxide) to form the diester derivative. A portion of the base oil per se and of the base oil containing 0.5% by weight of phenothiazine were tested in a standard Lauson engine test which was conducted by operating the engine at 1800 The oils were rated on a demerit system i 4 R. P. M. for 25 hours with a 1.5 indicated kilowatt load,

300 F. oil temperature and 295 F. water jacket temperature. The oils were rated by the demerit system described in connection with the C. F. R. test (Example III). The loss in weight of the copper-lead bearings was also determined. The results are shown in the following table.

Piston Cir-Pb skirt bearing Phenothiaziuc in Ca "Oxo adipate, wt. varnish weight loss percent demerit (g.

bearing) 1 Bearing failure at 22.5 hours.

Example V.-Chevrolet engine tests An S. A. E. grade mineral lubricant base oil (derived from acid-treated Mid-Continent lubricant stocks) was tested, with and without various additives, in a Chevrolet engine. The test, known as the Chevrolet L4 Test, was carried out for 36 hours. In one test the base oil contained 5% of a conventional detergent additive (termed herein Detergent Additive A) comprising calcium petroleum sulfonate and metal alkyl phenol sulfides. In another test, the oil contained 5% of Detergent Additive A and 0.5% by weight of phenothiazine. In another test, the oil contained 5% of Detergent Additive A and 0.5% by weight of the dioctyl phenothiazine of Example I. Varnish demerit ratings and loss in weight of copperlead hearings were determined for each run as follows:

Piston skirt Ou-Ib Additive in base oil varnish bearing demerit weight loss.

gJbearing None 9. 5 0.71 Additive A, 5%.. 2. 2 0. 39 Additive A, 5%; phenothiazine, 0.5% 2. 2 0. 09 Additive A, 5%; dioctyl phenothiazine, 0.5%. 1. 1 0. 37

Phenothiazine demonstrated corrosion inhibition properties but did not improve the detergency characteristics of the oil. The dialkyl phenothiazine, on the other hand, showed substantial detergent properties but no corrosion inhibition properties.

Example VIAluminum cup coking test An oil blend containing 0.5% of the dioctyl phenothiazine of Example I in the aviation base oil described in Example III was evaluated in the aluminum cup coking test. This test determines the efiectiveness of the additive as an inhibitor of coking under the severe temperature conditions generally encountered in aviation engines. The coking test was carried out by placing a desired amount of the base stock in an aluminum measuring cup and stirring while heat was applied. The side walls of the cup were maintained at a temperature of about 500 F. while the oil was heated from the bottom until'it reached a temperature of 550 F. The stirrer was then stopped for IO-minutes, followed by stirring for 10 minutes. The alternate non-stirring and stirring periods were The oil was then discarded and the coke deposit weighed.

A portion of the lubricant base oil containing no addi tive was also evaluated for comparative purposes. The results of the tests follow:

The dialkyl phenothiazine is a potent inhibitor for minimizing coking of mineral lubricating oils.

The lubricating oil base stocks used in the compositions of this invention may be straight mineral lubricating oils or distillates derived from parafiinic, naphthenic, asphaltic or mixed base crudes, or, if desired, various blended oils may be employed as well as residuals, particularly those from which asphaltic constituents have been carefully removed. The lubricating oil base stocks 20 will usually range from about 40 to 150 seconds (Saybolt) viscosity at 210 F. The viscosity index may range from 0 to 100 or even higher, although for aviation lubricants, which are the preferred base stocks in the practice of the present invention, the higher viscosity indexes are preferred.

What is claimed is:

1. A lubricant composition consisting essentially of a mineral oil and in the range of about 0.2 to 5.0% by weight of a compound having the following general formula:

wherein the R groups are alkyl radicals, each having in the range of 4 to 16 carbon atoms.

2. A composition as in claim 1 in which said R groups are identical and have in the range of 6 to 12 carbon atoms.

3. A composition as in claim 2 wherein said R groups. each contain 8 carbon atoms.

4. A composition as in claim 1 wherein said R groups are in the para positions.

5. A lubricating oil composition consisting essentially of a mineral lubricant base and in the range of 0.2 to 1.5 by weight of p,p'-diisooctyl phenothiazine.

References Cited in the file of this patent UNITED STATES PATENTS 2,006,756 Bartram July 2, 1935 2,190,648 Cantrell Feb. 20, 1940 2,587,660 Smith Mar. 4, 1952 2,609,343 Saunders et al. Sept. 2, 1952 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A MINERAL OIL AND IN THE RANGE OF ABOUT 0.2 TO 5.0% BY WEIGHT OF A COMPOUND HAVING THE FOLLOWING GENERAL FORMULA: 